1. Field of the Invention
The present invention relates to a method of forming oxide insulating films having excellent interface properties, which comprises depositing films by sputtering under irradiation of a light beam, more particularly to a method of forming oxide insulating films suitable as gate insulator films of insulated gate field-effect transistors (FETs) which are used in semiconductor integrated circuits and as driver devices of large-area liquid crystal displays, as well as insulator films of thin film semiconductor devices (e.g., photoelectric conversion devices) which are mounted on substrates. The present invention relates also to a method of forming an insulated gate field effect transistor comprising such an oxide insulating film and to a method of forming a capacitor comprising such an oxide insulating film.
2. Description of the Prior Art
Much attention is now paid to active devices or semiconductor integrated circuits (ICs) or capacitors which take advantage of oxide insulating films or oxide dielectric films fabricated by methods such as chemical vapor deposition (CVD). The insulating films (since the dielectric films of capacitors also are insulating films, the dielectric films of capacitors are referred to simply as insulator films or insulating films hereinafter, together with the insulating films of the ICs and the active devices) have been conventionally fabricated by a method such as CVD, which advantageously allows the films to be deposited at a temperature as low as 450.degree. C. or even lower, thus economizing on substrates by using those made of, for example, soda-lime glass or borosilicate glass.
As alternative methods for fabricating oxide insulating films at a low temperature comparable to that of CVD, there are also known depositing silicon oxide films by plasma-assisted CVD or by sputtering using a sputtering gas in which Ar atoms account for 80 to 100%.
Furthermore, there is also proposed fabricating silicon oxide films by photochemical vapor deposition, to use the films as gate oxide films of insulated gate field-effect transistors (FETs). This process is advantageous in that the film thus deposited achieves a density of interface states (interface level density) of about 2.times.10.sup.10 eV.sup.-1 cm.sup.-2 without suffering any damage which may be caused by the reaction with the underlying semiconductor or electrode material. However, it takes too long a time for the film deposition (i.e., too low in the film deposition rate) to be an industrially feasible process. The use of hydrogen also induces a hot-electron effect, which causes problems concerning the long reliability of the film.
In short, the insulating films thus fabricated by any of the conventional methods suffer a problem of having an unwanted density of interface states developed at the interfaces with the semiconductor layers, due to the presence of hydrogen or impurity, such as sodium, which functions as a fixed charge, or by the presence of a dangling bond.